1. Field of the Invention
This invention relates to an efficient xe2x80x9cnatural-typexe2x80x9d method of physically disrupting, under high pressures, starch-protein agglomerates in aqueous slurries of partially processed grains and non-cereal vegetable seeds by use of an apparatus, such as a microfluidizer, which imparts shear, cavitation, and impact. Deagglomeration under the conditions of the invention facilitates the isolation of starch and protein of high purity and quality, and renders possible the recovery of novel protein-starch combinations. Further, the invention is directed to starch and protein products obtained by the process.
2. Description of the Relevant Art
Commercial preparation of starch from grains such as rice has been practiced on a limited scale in the United States. Commercial preparation of rice starch has been described by Hogan (1967. In Starch: Chemistry and Technology, Whistler et al. (Eds.). Academic Press, Orlando, Fla., p. 65). There has been little change in the process since the 1960""s., e.g., the wet milling process for rice has remained essentially the same for decades. The process consists of steeping broken rice in 0.3-0.5% sodium hydroxide solution for a period of 24 hrs at room temperature to 50xc2x0 C. The steeped rice is ground or wet milled. The starch suspension is then stored for an additional 10-24 hrs followed by centrifugation to recover the starch which is further washed with water then dried. Protein is extracted and recovered by neutralization with acid to the isoelectric pH of protein (pH 6.4). The precipitate is allowed to settle and is recovered in filter presses or centrifuges (Cagampang, et al. 1966. Cereal Chem. 43: 145). Although this process for the separation of rice starch and rice protein has been well known and practiced in the art, certain disadvantages have been found to be associated with these types of processes. The disadvantages are that the sodium hydroxide degrades the protein component leading to the formation of small peptides which can cause bitterness and thus a product not suitable for human consumption, that these processes are water-, energy-, and time-intensive and require costly treatment of the wastewater generated, and further, that usage of alkali and the resulting salt disposal problem is an environmental concern.
A number of other laboratory methods have been used for rice starch and protein separation (Hogan, J. T., supra; Juliano, B. O. 1984. In Starch: Chemistry and Technology, 2nd Edition, Whistler et al. (Eds.). Academic Press, Orlando, Fla., pp. 507-525). In addition, rice starch and protein can also be separated by use of an emulsifier (Kung et al. 1987. J. Chinese Agri. Chem. Soc. 25: 299-307). More recently, Bartsch et al. also described a process of recovering starch and protein from rice which involves comminuting under wet or dry conditions, soaking in an aqueous solution at pH 9, adding enzymes before or during soaking, and homogenizing during or after soaking (DE4428933, Feb. 22, 1996). The homogenization is carried out under indeterminate pressure conditions in an ultrasound device, a microcavitation disintegration apparatus, a colloidal mill, or a procedure involving screening combined with a displacement pump.
Several techniques of isolation of starch and protein from corn and other grain products have been disclosed in the patent literature, but these too are associated with certain disadvantages. Most of the isolation techniques are related to corn wet milling and use chemicals to extract the protein fraction. Two patented processes which are drawn to the physical aspects of starch-protein matrix breakdown are Kampen (U.S. Pat. No. 5,410,021, Apr. 25, 1995) and Huster et al. (U.S. Pat. No. 4,416,701, Nov. 22, 1983).
Kampen describes the process of mechanically breaking protein starch down by wet attrition milling. The grain particles, specifically corn, are milled to particle size sufficiently small to break the bond between starch and protein and sufficiently large to retain substantially all of the starch granules intact. The protein is then extracted with ethanol and alkali solvents, separated and dried to form protein and/or protein isolate. The intact starch granules are cleaned and dried. The attrition mill described in the patent consists of two carborundum disks with one rotating at a high speed and the other stationary. The particle size reduction is limited to the clearance between the disks; therefore, once the clearance is set at more than the particle size of the largest granule, separation of smaller granules still imbedded in the protein matrix will not take place. The process relies on chemical extraction of protein to produce intact starch granules.
Huster et al. describe a wet process of a communation of the steeped raw material in a high pressure apparatus equipped with a splitter head or a disintegration valve. The process differed from earlier procedures in that the steeping process was performed under low pressure (145-218 psi) thereby considerably shortening the steeping time to three hours or less and the steeped material was then subjected to an optimum pressure of 1450 psi in a high pressure apparatus equipped with a splitter head or disintegration valve. The certain drop in pressure produced by passing a material through a small slit subjects it to high acceleration and considerable impact and mechanical strain. Pressures of at least 145 psi and an optimum pressure of 1450 psi are recommended for breakdown of morphological structure between starch grain and protein matrix. Further, in the case of corn, the use of the splitter head required multiple passes for complete disintegration.
Later studies by the group (Meuser et al. 1986. Cereals in a European Context/First Eur. Conf. On Food Sci., pages 285-299; Meuser et al. 1985. New Approaches to Research on Cereal Carbohydrates, Hill et al., Eds. Elsevier Science Publishers, Amsterdam, The Netherlands, pages 161-180) disclose that a steeping time of 12 hours at atmospheric pressure or 4 hrs at 218 psi, sometimes in the presence of SO2, is required for corn and other grains and vegetables prior to high pressure (1450 psi) processing in the splitter head apparatus and that the distribution of particle sizes changes after multiple passes through the disintegration valve. The first passage through the disintegration valve results in most particles being concentrated in the 28-160 xcexcm range, the second passage results in 8% of the fraction being particles greater than 63 xcexcm, and after the fourth passage, particles were observed to be at different stages of decomposition, ranging from intact particles to complete structural disintegration. Further, this technology using low pressure homogenization might not be suitable for the production of rice starches due to the small granule size and the different chemistry of the starch-protein matrix.
Rice products are used in many applications, particularly as food ingredients. Rice starch is useful for, among other uses, to improve texture, to maintain freeze-thaw stability, and to improve moisture retention of food products. Rice starch is used as a fat mimetic to reduce fat and caloric content in food products. Rice products are used in baby food preparation based on their digestibility and absence of gluten. Rice protein, in its non-degraded form, is both hypo-allergenic and nutritionally valuable. Being a very fine powder, rice starch also has other applications including use as a cosmetic dusting powder, laundry stiffening agent, paper and photographic paper powder, sugar coating, confectionary, and excipient for pharmaceutical tablets.
The quality of the starch recovered from grains such as rice or some vegetables is determined by the amount of residual protein, by the relative absence of starch-starch and starch-protein agglomerates, and by a low percentage of starch damage. For example, for rice starch to perform best as a fat mimetic, the starch should be predominantly present in the form of individual granules. If a physical process of separation for rice flour, for example, could be developed in which the rice protein could be separated from the starch without contact with chemicals and without embitterment, the existence of a second value-added product would improve the overall economics of the production process. The successful development of a commercial process to manufacture a reasonably priced xe2x80x9call naturalxe2x80x9d rice starch and rice protein would allow for the development of a new industry and new markets for rice.
We have discovered that slurries of amylaceous flour from milled seed, which contain dispersed particles of starch-protein and starch-starch agglomerates, can be subjected to high pressure processing to obtain deagglomerated starch and protein. The resultant deagglomerated material is essentially individual, intact starch granules and protein homogeneously dispersed in a liquid matrix. The substantially unadulterated condition of the deagglomerated materials is such that they can be further treated to yield starch and protein fractions of a high purity, improved quality, and superior market value as compared to fractions produced by other methods.
In accordance with this discovery, it is an object of the invention to provide a novel high pressure process for the treatment of partially processed grains and vegetables which results in the deagglomeration of the starch and the protein while still ensuring and maintaining the integrity and quality of the two components, starch and protein. It is an object of the invention to provide a method for processing a starch slurry under high pressures, a method wherein starch containing agglomerated particles are deagglomerated and then individual starch granules and the protein resulting from the deagglomeration are homogeneously dispersed in a liquid matrix. Amongst other things, the product resulting from the deagglomeration procedure can be utilized in its aqueous form, dried to a fine powder, or further subjected to separation procedures, as for example, density-based or particle size separation techniques to yield the recovery of starch and protein fractions. In particular, a method is provided by which rice slurry containing starch-starch and starch-protein agglomerates is subjected to processing in a microfluidizer resulting in deagglomerated rice starch granules and rice protein homogeneously dispersed in a liquid matrix.
In a preferred embodiment of the invention, waxy and non-waxy rice is treated to yield a rice starch and protein.
Other objects and advantages of the invention will become readily apparent from the following description.